1. Field of the Invention
The present invention relates to a generalized phase shift based precoding method or an extended phase shift based precoding method in a multiple-antenna system using a plurality of subcarriers and a transceiver for supporting the same.
2. Discussion of the Related Art
Recently, as information communication services have been popularized, a variety of multimedia services has appeared, and high-quality services have appeared, a requirement for a wireless communication service is rapidly increasing. In order to actively cope with such a tendency, a method of increasing communication capacity in a wireless communication environment may include a method of finding a new available frequency band and a method of increasing the efficiency of a restricted resource. As the latter method, multiple-antenna transmission/reception technologies of mounting a plurality of antennas in a transmitter/receiver and further ensuring a space for using a resource to obtain a diversity gain or transmitting data via the antennas in parallel to increase transmission capacity are attracting much attention and are being actively developed.
Among the multiple-antenna transmission/reception technologies, the general structure of a multiple-input multiple-output system using an orthogonal frequency division multiplexing (OFDM) will now be described with reference to FIG. 1.
In a transmitter, a channel encoder 101 adds redundancy bits to transmission data bits to reduce influence due to a channel or noise, a mapper 103 converts data bit information into data symbol information, a serial/parallel converter 105 converts data symbols into parallel data symbols to be carried in a plurality of subcarriers, and a multiple-antenna encoder 107 converts the parallel data symbols into space-time signals. A multiple-antenna decoder 109, a parallel/serial converter 111, a demapper 113, and a channel decoder 115 included in a receiver perform the inverse functions of the multiple-antenna encoder 107, the serial/parallel converter 105, the mapper 103, and the channel encoder 101, respectively.
In a multiple-antenna OFMD system, a variety of technologies of increasing data transmission reliability is required. Among them, a scheme for increasing the spatial diversity gain includes a space-time code (STC) and a cyclic delay diversity (CDD) and a scheme for increasing a signal-to-noise ratio (SNR) includes a beamforming (BF) and a Precoding. The STC and the CDD are used to increase the transmission reliability of an open loop system in which a transmitter cannot use feedback information, and the BF and the Precoding are used to maximize the SNR using feedback information in a closed loop system in which a transmitter can use the feedback information.
Among these schemes, the scheme for increasing the spatial diversity gain and the scheme for increasing the SNR, and more particularly, the CDD and the Precoding, will now be described.
In the CDD, a system having a plurality of transmission antennas transmits OFDM signals having different delays or different levels via all the antennas such that a receiver obtains a frequency diversity gain. FIG. 2 shows the configuration of a multiple-antenna system using the CDD.
The OFDM symbols are divided and transmitted to the antennas through the serial/parallel converter and the multiple-antenna encoder, and are added to a cyclic prefix (CP) for preventing inter-channel interference to be transmitted to the receiver. Where, a data sequence sent to a first antenna is transmitted to the receiver without change, and a data sequence sent to a next antenna is cyclic-delayed from the sequence sent to the previous antenna by predetermined bits and is then transmitted to the receiver.
Meanwhile, if the CDD is implemented in a frequency domain, the cyclic delay may be expressed by a product of phase sequences. That is, as shown in FIG. 3, data sequences in the frequency domain are multiplied by predetermined different phase sequences (phase sequence 1 to phase sequence M) according to the antennas, and are subjected to an inverse fast Fourier transform (IFFT), thereby being transmitted to the receiver. This is called a phase shift diversity.
If the phase shift diversity is used, it is possible to change a flat fading channel to a frequency-selective channel and to obtain a frequency diversity gain through a channel code or to obtain a multiple-user diversity gain through frequency-selective scheduling.
Meanwhile, the Precoding includes a codebook based precoding which is used when feedback information is finite in a closed loop system and a scheme for quantizing and feeding back channel information. Among them, in the codebook based precoding, the index of a precoding matrix which is previously known to a transmitter/receiver is transmitted to the transmitter as s feedback information to obtain a SNR gain.
FIG. 4 shows the configuration of the transmitter/receiver of a multiple-antenna system using the codebook based precoding. The transmitter and the receiver have finite precoding matrixes P1 to PL. The receiver feeds back an optimal precoding matrix index 1 using channel information and the transmitter applies a precoding matrix corresponding to the feed-back index to transmission data X1 to XMt. Table 1 shows an example of the codebook which is applicable when 3-bit feedback information is used in an IEEE 802.16e system which supports a spatial multiplexing rate of 2 and has two transmission antennas.
TABLE 1Matrixindex(binary)Column1Column200010010010.7940−0.5801 − j0.1818−0.5801 + j0.1818  −0.79400100.7940  0.0576 − j0.60510.0576 + j0.6051−0.79400110.7941−0.2978 + j0.5298−0.2978 − j0.5298  −0.79411000.7941  0.6038 − j0.06890.6038 + j0.0689−0.79411010.3289  0.6614 − j0.67400.6614 + j0.6740−0.32891100.5112  0.4754 + j0.71600.4754 − j0.7160−0.51121110.3289−0.8779 + j0.3481−0.8779 − j0.3481  −0.3289
The phase shift diversity (PSD) is attracting much attention because a frequency-selective diversity gain can be obtained in an open loop system and a frequency-selective scheduling gain can be obtained in a closed loop system in addition to the above-described advantages. However, since a spatial multiplexing rate is 1, a high data transmission rate cannot be obtained. In addition, when resource allocation is fixed, it is difficult to obtain the above-described gains.
In addition, since the above-described codebook based precoding can use a high spatial multiplexing rate while requiring a small amount of feedback information (index information), it is possible to efficiently transmit data. However, since a stable channel for feedback should be ensured, the codebook based precoding is not suitable for an environment, in which channel variation is excessive, and is applicable to only a closed loop system.